Methionine requirement of the enterally fed term infant in the first month of life in the presence of cysteine

Low-Protein Infant Formula and Obesity Risk

Infant formulas have been designed to mimic human milk for infants who cannot be breastfed. The overall goal is to establish similar functional outcomes to assure optimal growth, development, maturation of the immune system, and programming of the metabolic system. However, after decades of improving infant formula, growth patterns and body composition development are still different in formula-fed infants compared to breastfed infants, which could contribute to an increased risk of obesity among formula-fed infants. It has been hypothesized that the lower protein concentration of breast milk compared to infant formula influences infants’ growth and body composition. Thus, several trials in formula-fed infants with different protein intake levels have been performed to test this hypothesis. In this review, we discuss the current evidence on low-protein infant formula and obesity risk, including future perspectives and implications.

Untargeted Metabolomic Analysis of Human Milk from Mothers of Preterm Infants

The application of metabolomics in neonatology offers an approach to investigate the complex relationship between nutrition and infant health. Characterization of the metabolome of human milk enables an investigation into nutrients that affect the neonatal metabolism and identification of dietary interventions for infants at risk of diseases such as necrotizing enterocolitis (NEC). In this study, we aimed to identify differences in the metabolome of breast milk of 48 mothers with preterm infants with NEC and non-NEC healthy controls. A minimum significant difference was observed in the human milk metabolome between the mothers of infants with NEC and mothers of healthy control infants. However, significant differences in the metabolome related to fatty acid metabolism, oligosaccharides, amino sugars, amino acids, vitamins and oxidative stress-related metabolites were observed when comparing milk from mothers with control infants of ≤1.0 kg birth weight and >1.5 kg birth weight. Understanding the functional biological features of mothers’ milk that may modulate infant health is important in the future of tailored nutrition and care of the preterm newborn.

Long-term effects of a modified, low-protein infant formula on growth and body composition: Follow-up of a randomized, double-blind, equivalence trial

BACKGROUND & AIM

High protein intake in early life is associated with an increased risk of childhood obesity. Feeding a modified lower-protein (mLP) infant formula (1.7 g protein/100 kcal) until the age of 6 months is safe and supports adequate growth. The aim of the present study is to assess longer-term anthropometry with BMI at 1 and 2 years as primary outcome parameter and body composition in children fed mLP formula.

METHODS

Healthy term-born infants received mLP or control formula (CTRL) (2.1 g protein/100 kcal) until 6 months of age in a double-blinded RCT. A breast-fed (BF) group served as a reference. Anthropometry data were obtained at 1 and 2 years of age. At the age of 2 years, body composition was measured with air-displacement plethysmography. Groups were compared using linear mixed model analysis.

RESULTS

At 1 and 2 years of age, anthropometry, including BMI, and body composition did not differ between the formula groups (n = 74 mLP; n = 69 CTRL). Compared to the BF group (n = 51), both formula-fed groups had higher z scores for weight for age, length for age, waist circumference for age, and mid-upper arm circumference for age at 1 year of age, but not at 2 years of age (except for z score of weight for age in the mLP group). In comparison to the BF group, only the mLP group had higher fat mass, fat-free mass, and fat mass index. However, % body fat did not differ between feeding groups.

CONCLUSIONS

In this follow-up study, no significant differences in anthropometry or body composition were observed until 2 years of age between infants fed mLP and CTRL formula, despite the significantly lower protein intake in the mLP group during the intervention period. The observed differences in growth and body composition between the mLP group and the BF reference group makes it necessary to execute new trials evaluating infant formulas with improved protein quality together with further reductions in protein content.

CLINICAL TRIAL REGISTRY

This trial was registered in the Dutch Trial Register (Study ID number NTR4829, trial number NL4677). https://www.trialregister.nl/trial/4677.

Methionine Nutrition and Metabolism: Insights from Animal Studies to Inform Human Nutrition

Methionine is a nutritionally indispensable amino acid, and is unique among indispensable amino acids due to its sulfur atom. Methionine is involved in cysteine synthesis via the transsulfuration pathway, which is rate limiting for the key antioxidant molecule, glutathione. Methionine is also the primary methyl donor in the body through S-adenosylmethionine via the transmethylation pathway, which is involved in the synthesis of several key metabolites including creatine and phosphatidylcholine. Methionine can also be remethylated from homocysteine, in the presence of betaine via choline and/or folate. Thus methionine demands from a dietary perspective are regulated not only by the presence of cysteine in the body, but also by the demands in vivo for the various metabolites formed from it, and also by the presence of these compounds in foods. Indeed, methionine, cysteine, and the various methyl donors/acceptors vary in human foods, and thus regulate methionine availability, especially under conditions of growth and development. Much of our understanding of methionine nutrition and metabolism arises from experiments in animal models. This is because most animal feed formulations are plant-based and plant sources are relatively low in methionine and cysteine amounts. Thus, this brief review will touch on some broad aspects of human methionine nutrition, including requirements in different life stages, disease, and bioavailability, with some examples from the insights/lessons learned from experiments initially conducted in animals.

Lessons Learned from Inherited Metabolic Disorders of Sulfur-Containing Amino Acids Metabolism

The metabolism of sulfur-containing amino acids (SAAs) requires an orchestrated interplay among several dozen enzymes and transporters, and an adequate dietary intake of methionine (Met), cysteine (Cys), and B vitamins. Known human genetic disorders are due to defects in Met demethylation, homocysteine (Hcy) remethylation, or cobalamin and folate metabolism, in Hcy transsulfuration, and Cys and hydrogen sulfide (H2S) catabolism. These disorders may manifest between the newborn period and late adulthood by a combination of neuropsychiatric abnormalities, thromboembolism, megaloblastic anemia, hepatopathy, myopathy, and bone and connective tissue abnormalities. Biochemical features include metabolite deficiencies (e.g. Met, S-adenosylmethionine (AdoMet), intermediates in 1-carbon metabolism, Cys, or glutathione) and/or their accumulation (e.g. S-adenosylhomocysteine, Hcy, H2S, or sulfite). Treatment should be started as early as possible and may include a low-protein/low-Met diet with Cys-enriched amino acid supplements, pharmacological doses of B vitamins, betaine to stimulate Hcy remethylation, the provision of N-acetylcysteine or AdoMet, or experimental approaches such as liver transplantation or enzyme replacement therapy. In several disorders, patients are exposed to long-term markedly elevated Met concentrations. Although these conditions may inform on Met toxicity, interpretation is difficult due to the presence of additional metabolic changes. Two disorders seem to exhibit Met-associated toxicity in the brain. An increased risk of demyelination in patients with Met adenosyltransferase I/III (MATI/III) deficiency due to biallelic mutations in the MATIA gene has been attributed to very high blood Met concentrations (typically >800 μmol/L) and possibly also to decreased liver AdoMet synthesis. An excessively high Met concentration in some patients with cystathionine β-synthase deficiency has been associated with encephalopathy and brain edema, and direct toxicity of Met has been postulated. In summary, studies in patients with various disorders of SAA metabolism showed complex metabolic changes with distant cellular consequences, most of which are not attributable to direct Met toxicity.

Nuclear Magnetic Resonance-Based Metabolomic Comparison of Breast Milk and Organic and Traditional Formula Milk Brands for Infants and Toddlers

In recent years, new formula milk (FM) products based on milk from farms that strictly adhere to the "organic farming" practices became available. However, little is known about the differences in nutritional profile of these organic formulae with respect to traditional ones. We comprehensively evaluated the metabolite profiles of FM with nuclear magnetic resonance (NMR)-based metabolomic analysis. Five commercial brands of organic and nonorganic formula liquid milk for infants (0-12 months) and toddlers (1-3 years) were analyzed, together with human milk (HM) samples. Proton NMR (¹H NMR) spectroscopy mapped molecular characteristics of FM linked to different production techniques, and identified differences between FM and HM samples. We performed a metabolic fingerprint analysis using multivariate and univariate statistical techniques. A clear distinction is found among different commercial brands of the FM samples. In addition, several differences in metabolomic profiles of FM have been found in comparison with HM for the first time. Notably, it was possible to identify, both in the formulations for toddlers and for infants, metabolites that vary in concentration between the formulae produced with milk obtained according to organic farming techniques, and those produced using nonorganic milk. In particular, organic and nonorganic formulations are differentiated by the levels of glucose, methionine, o-phosphocholine, butyrate, hippurate, creatine, and dimethyl sulfone. Importantly, the HM appeared to differ from both organic and nonorganic brands in a context of metabolites. These findings inform efforts to design FM in ways that closely mimic HM, and guide research to differentiate organic and traditional FM.

A modified low-protein infant formula supports adequate growth in healthy, term infants: a randomized, double-blind, equivalence trial

BACKGROUND

A high protein intake in early life is associated with a risk of obesity later in life. The essential amino acid requirements of formula-fed infants have been reassessed recently, enabling a reduction in total protein content and thus in protein intake.

OBJECTIVES

We aimed to assess the safety of an infant formula with a modified amino acid profile and a modified low-protein (mLP) content in healthy term-born infants. Outcomes were compared with a specifically designed control (CTRL) infant formula.

METHODS

In this double-blind, randomized controlled equivalence trial, infants received either mLP (1.7 g protein/100 kcal; n = 90) or CTRL formula (2.1 g protein/100 kcal; n = 88) from enrollment (age ≤ 45 d) to 6 mo of age. A breastfed group served as a reference (n = 67). Anthropometry and body composition were determined at baseline, 17 wk (including safety blood parameters), and 6 mo of age. The primary outcome was daily weight gain from enrollment up until the age of 17 wk (at an equivalence margin of ±3.0 g/d).

RESULTS

Weight gain from baseline (mean ± SD age: 31 ± 9 d) up to the age of 17 wk was equivalent between the mLP and CTRL formula groups (27.9 and 28.8 g/d, respectively; difference: -0.86 g/d; 90% CI: -2.36, 0.63 g/d). No differences in other growth parameters, body composition, or in adverse events were observed. Urea was significantly lower in the mLP formula group than in the CTRL formula group (-0.74 mmol/L; 95% CI: -0.97, -0.51 mmol/L; P < 0.001). Growth rates, fat mass, fat-free mass, and several essential amino acids were significantly higher in both formula groups than in the breastfed reference group.

CONCLUSIONS

Feeding an infant formula with a modified amino acid profile and a lower protein content from an average age of 1 mo until the age of 6 mo is safe and supports an adequate growth, similar to that of infants consuming CTRL formula. This trial was registered at www.trialregister.nl as Trial NL4677.

Growth and Clinical Variables in Nitrogen-Restricted Piglets Fed an Adjusted Essential Amino Acid Mix: Effects of Partially Intact Protein-Based Diets

Background

Current recommendations for protein levels in infant formula are intended to ensure that growth matches or exceeds growth of breastfed infants, but may provide a surplus of amino acids (AAs). Recent infant studies with AA-based formulas support specific adjustment of the essential amino acid (EAA) composition allowing for potential lowering of total protein levels. With the use of a combination of intact protein and free EAAs, we designed a formula that meets these adjusted EAA requirements for infants.

Objective

Our objective was to test whether this adjusted formula is safe and supports growth in a protein-restricted piglet model, and whether it shows better growth than an isonitrogenous formula based on free AAs.

Methods

Term piglets (Landrace × Yorkshire × Duroc, n = 72) were fed 1 of 4 isoenergetic formulas containing 70% intact protein and 30% of an EAA mixture or a complete AA-based control for 20 d: standard formula (ST-100), ST-100 with 25% reduction in proteinaceous nitrogen (ST-75), ST-75 with an adjusted EAA composition (O-75), or a diet as O-75, given as a complete AA-based diet (O-75AA).

Results

After an initial adaptation period, ST-75 and O-75 pigs showed similar growth rates, both lower than ST-100 pigs (∼25 compared with 31 g · kg-1 · d-1, respectively). The O-75AA pigs showed further reduced growth rate (15 g · kg-1 · d-1) and fat proportion (both P < 0.05, relative to O-75).

Conclusions

Formula based partly on intact protein is superior to AA-based formula in this experimental setting. The 25% lower, but EAA-adjusted, partially intact protein-based formula resulted in similar weight gain with a concomitant increased AA catabolism, compared with the standard 25% lower standard formula in artificially reared, protein-restricted piglets. Further studies should investigate if and how the specific EAA adjustments that allow for lowering of total protein levels will affect growth and body composition development in formula-fed infants.

Growth and Clinical Variables in Nitrogen-Restricted Piglets Fed an Adjusted Essential Amino Acid Mix: Effects of Free Amino Acid-Based Diets

Background

Excess protein intake in early life has been linked to obesity and metabolic syndrome in later life. Yet protein, and in particular the essential amino acids (EAAs), need to be present in adequate quantity to support growth.

Objective

With the use of a piglet model restricted in dietary amino acids (AAs), we compared the efficacy and safety of a standard formula with a low-AA formula containing an adjusted AA composition.

Methods

Female piglets (3-7 d old; Landrace × Yorkshire × Duroc) were fed 1 of 4 isoenergetic AA-based formulas for 14 d (700 kJ · kg body weight-1 · d-1). The formulas contained a set control amount (44 g/L) and AA compositions referred to as the experimental standard (ST-100, n = 22), or 20% or 50% lower total AAs (respectively, ST-80, n = 19 and ST-50, n = 13), or 20% lower total AAs with an optimally adjusted EAA composition (O-80, n = 17). A series of clinical and paraclinical endpoints were measured.

Results

Growth rates were similar for ST-100, O-80 and ST-80 piglets (all ∼15 g · kg-1 · d-1), whereas ST-50 had a markedly lower weight gain relative to all groups (all P < 0.05). Relative to ST-100, all groups with reduced AA intake showed ∼16% reduction in plasma albumin and ∼30% reduction in plasma urea (both P < 0.05). The absolute leucine oxidation rate was ∼30% lower for O-80 than for ST-100 piglets (P < 0.05).

Conclusions

These data show that a 20% reduction in total AA intake for both the control (ST-80) and the adjusted AA (O-80) formula did not have any short-term adverse effects on growth in artificially reared, AA-restricted piglets. The lower absolute leucine oxidation rate observed in O-80 supports the development of an infant formula with an improved AA composition and a moderate reduction in total protein to support adequate growth in healthy infants.

The Pediatric Methionine Requirement Should Incorporate Remethylation Potential and Transmethylation Demands

The metabolic demand for methionine is great in neonates. Indeed, methionine is the only indispensable sulfur amino acid and is required not only for protein synthesis and growth but is also partitioned to a greater extent to transsulfuration for cysteine and taurine synthesis and to >50 transmethylation reactions that serve to methylate DNA and synthesize metabolites, including creatine and phosphatidylcholine. Therefore, the pediatric methionine requirement must accommodate the demands of rapid protein turnover as well as vast nonprotein demands. Because cysteine spares the methionine requirement, it is likely that the dietary provision of transmethylation products can also feasibly spare methionine. However, understanding the requirement of methionine is further complicated because demethylated methionine can be remethylated by the dietary methyl donors folate and betaine (derived from choline). Intakes of dietary methyl donors are highly variable, which is of particular concern for newborns. It has been demonstrated that many populations have enhanced requirements for these nutrients, and nutrient fortification may exacerbate this phenomenon by selecting phenotypes that increase methyl requirements. Moreover, higher transmethylation rates can limit methyl supply and affect other transmethylation reactions as well as protein synthesis. Therefore, careful investigations are needed to determine how remethylation and transmethylation contribute to the methionine requirement. The purpose of this review is to support our hypothesis that dietary methyl donors and consumers can drive methionine availability for protein synthesis and transmethylation reactions. We argue that nutritional strategies in neonates need to ensure that methionine is available to meet requirements for growth as well as for transmethylation products.

Cereals and pulse-based ready-to-use therapeutic food as an alternative to the standard milk- and peanut paste-based formulation for treating severe acute malnutrition: a noninferiority, individually randomized controlled efficacy clinical trial

BACKGROUND

The cost of current standard ready-to-use therapeutic food (RUTF) is among the major obstacles to scaling up community-based management of acute malnutrition (CMAM), an important child survival strategy. Identifying a cheaper alternative is a global public health priority.

OBJECTIVE

We sought to compare the efficacy of soya-maize-sorghum RUTF (SMS-RUTF) with that of standard peanut paste-based RUTF (P-RUTF).

DESIGN

We used a nonblinded, parallel-group, simple randomized controlled trial along with a day care approach that enrolled 2 groups of children aged 6-23 and 24-59 mo, respectively, with severe acute malnutrition (SAM).

RESULTS

Intention-to-treat (ITT) and per-protocol (PP) analyses showed noninferiority of SMS-RUTF compared with P-RUTF for the recovery rate [ITT: Δ = -2.0% (95% CI: -7.6%, 3.6%); PP: -1.9% (95% CI: -5.3%, 1.4%)], weight gain [Δ = -0.7 g · kg(-1)· d(-1)(95% CI: -1.3, 0.0 g · kg(-1)· d(-1))], and length of stay [Δ = 2.0 d (95% CI: -1.7, 5.8 d)] in children ≥24 mo of age. In children ≤23 mo of age, the recovery rate of SMS-RUTF was inferior to that of P-RUTF [ITT: Δ = -20.8% (95% CI: -29.9%, -11.7%); PP: -17.2% (95% CI: -25.6%, -8.7%)]. Treatment with SMS-RUTF resulted in a greater increase in hemoglobin [0.670 g/dL (95% CI: 0.420, 0.921 g/dL);P< 0.001]. Treatment with both RUTFs resulted in the replenishment of all of the amino acids tested except for methionine. There were no differences at discharge between RUTF groups in fat mass [Δ = 0.3 kg (95% CI: -0.6, 1.6 kg);P= 0.341] or fat mass index [Δ = 0.4 kg/m(2)(95% CI: -0.3, 1.1 kg/m(2));P= 0.262]. By contrast, comparisons of fat-free mass indicated lower concentrations than the community controls after treatment with either of the 2 RUTFs [Δ = -1.3 kg (95% CI: -2.4, -0.1 kg) andP= 0.034 for comparison between community controls and the SMS-RUTF group; Δ = -1.8 kg (95% CI: -2.9, -0.6 kg) andP= 0.003 for comparison between community controls and the P-RUTF group].

CONCLUSION

SMS-RUTF can be used to treat SAM in children aged ≥24 mo to reduce the costs of CMAM programs. More research is required to optimize SMS-RUTF for younger children. This trial was registered in the Pan African Clinical Trial Registry as PACTR201303000475166.

Protein Concentration in Milk Formula, Growth, and Later Risk of Obesity: A Systematic Review

BACKGROUND

Protein intake may influence important health outcomes in later life.

OBJECTIVE

The objective of this study was to investigate current evidence on the effects of infant formulas and follow-on formulas with different protein concentrations on infants' and children's growth, body composition, and later risk of overweight and obesity.

METHODS

In this systematic review, we searched electronic databases (including MEDLINE, Embase, and the Cochrane Library) up until November 2014 for randomized controlled trials (RCTs). Eligible studies had to include children aged 0-3 y who represented the general population and were fed cow milk-based infant formulas with variations in protein concentration. Control groups received lower-protein cow milk-based formulas (as defined by the authors). The primary outcomes were growth, overweight, obesity, and adiposity. Various time points for outcomes assessment were accepted for inclusion. If possible, a meta-analysis was performed.

RESULTS

Twelve RCTs met our inclusion criteria. Different formula protein concentrations did not affect linear growth other than a transient effect on mean length at 3 mo observed in a meta-analysis of 4 studies (mean difference, - 0.27 cm; 95% CI: -0.52, -0.02). Lower mean weight and weight z scores obtained from the infants fed lower-protein formulas were observed only from 6 to 12 mo of age. Data from one large RCT showed that consumption of a lower-protein infant formula may reduce body mass index at 12 mo of age and later (12 mo, 24 mo, and 6y) and the risk of obesity at 6 y. Effects on body composition remained unclear.

CONCLUSIONS

The current evidence is insufficient for assessing the effects of reducing the protein concentration in infant formulas on long-term outcomes, but, if confirmed, this could be a promising intervention for reducing the risk of overweight and obesity in children. In view of the limited available evidence, more studies replicating effects on long-term health outcomes are needed.

The dynamics of methionine supply and demand during early development

Methionine is an indispensable amino acid that, when not incorporated into protein, is converted into the methyl donor S-adenosylmethionine as entry into the methionine cycle. Following transmethylation, homocysteine is either remethylated to reform methionine or irreversibly trans-sulfurated to form cysteine. Methionine flux to transmethylation and to protein synthesis are both high in the neonate and this review focuses on the dynamics of methionine supply and demand during early development, when growth requires expansion of pools of protein and transmethylation products such as creatine and phosphatidylcholine (PC). The nutrients folate and betaine (derived from choline) donate a methyl group during remethylation, providing an endogenous supply of methionine to meet the methionine demand. During early development, variability in the dietary supply of these methionine cycle-related nutrients can affect both the supply and the demand of methionine. For example, a greater need for creatine synthesis can limit methionine availability for protein and PC synthesis, whereas increased availability of remethylation nutrients can increase protein synthesis if dietary methionine is limiting. Moreover, changes to methyl group availability early in life can lead to permanent changes in epigenetic patterns of DNA methylation, which have been implicated in the early origins of adult disease phenomena. This review aims to summarize how changes in methyl supply and demand can affect the availability of methionine for various functions and highlights the importance of variability in methionine-related nutrients in the infant diet.

Threonine Requirement of the Enterally Fed Term Infant in the First Month of Life

OBJECTIVE

Threonine is one of the essential amino acids. Its major fate is incorporation into intestinal mucosal proteins and synthesis of secretory glycoproteins. Therefore, it has an important function in the neonatal gut barrier integrity. The objective was to quantify the threonine requirement in fully enterally fed term neonates by means of the indicator amino acid oxidation (IAAO) method, using L-[1-C]phenylalanine as indicator.

METHODS

After a 24-hour test diet adaptation, containing randomly assigned amounts of threonine (range 5-182 mg · kg · day), the participating neonates received a primed continuous infusion of [C]bicarbonate and L-[1-C]phenylalanine. At baseline and during the plateau phase of both infusions, breath samples were obtained for CO2. The fractional L-[1-C]phenylalanine oxidation (FCO2) was estimated and plotted against the threonine intakes. Biphasic linear regression crossover analysis was used to calculate the breakpoint of the FCO2, representing the mean threonine requirement. Data are presented as mean ± SD.

RESULTS

Thirty-two term neonates (gestational age 39 ± 1 weeks, birth weight 3.3 ± 0.3 kg, mean postnatal age 10 ± 4 days) were studied. The mean threonine requirement was estimated to be 68 mg · kg · day with an upper and lower 95% confidence interval of 104 and 32 mg · kg · day, respectively (r = 0.37).

CONCLUSIONS

The determined threonine requirement is extremely close to the existing requirement recommendations (∼90% of the present World Health Organization requirement guidelines). Infant formula preparations presently on the market, however, contain up to twice as much threonine as recommended. The threonine intake in formula-fed infants may therefore be reduced considerably.

L-Cysteine metabolism and its nutritional implications

L-Cysteine is a nutritionally semiessential amino acid and is present mainly in the form of L-cystine in the extracellular space. With the help of a transport system, extracellular L-cystine crosses the plasma membrane and is reduced to L-cysteine within cells by thioredoxin and reduced glutathione (GSH). Intracellular L-cysteine plays an important role in cellular homeostasis as a precursor for protein synthesis, and for production of GSH, hydrogen sulfide (H(2)S), and taurine. L-Cysteine-dependent synthesis of GSH has been investigated in many pathological conditions, while the pathway for L-cysteine metabolism to form H(2)S has received little attention with regard to prevention and treatment of disease in humans. The main objective of this review is to highlight the metabolic pathways of L-cysteine catabolism to GSH, H(2)S, and taurine, with special emphasis on therapeutic and nutritional use of L-cysteine to improve the health and well-being of animals and humans.

Phenylalanine requirements of enterally fed term and preterm neonates

BACKGROUND

Phenylalanine, which is an essential aromatic amino acid, is either used for protein synthesis or irreversibly hydroxylated to tyrosine. The provision of optimal amounts of dietary phenylalanine is not only important for growth and development but might also influence catecholamine synthesis and release rates. The current recommended aromatic amino acid requirement for infants aged 0-6 mo is based on the amino acid content of human milk.

OBJECTIVE

We quantified the requirements for phenylalanine in the presence of excess tyrosine (166 or 177 mg/kg per day for term and preterm infants, respectively) for term and preterm neonates by using the indicator amino acid oxidation method with l-[1-(13)C]lysine 2HCl as an indicator. Hence, we determined the minimum obligatory phenylalanine requirement.

DESIGN

Fully enterally fed term and preterm infants received randomly graded amounts of phenylalanine (5-177 mg/kg per day) as part of an elemental formula. Data are expressed as means ± SDs.

RESULTS

Twenty term (birth weight: 3.19 ± 0.34 kg; gestational age: 38.9 ± 1 wk) and 16 preterm (birth weight: 1.75 ± 0.17 kg; gestational age: 32.5 ± 0.6 wk) Asian infants participated at a postnatal age of 17 ± 8 d. In total, 44 studies were performed. The minimum obligatory phenylalanine requirement was 58 mg/kg per day (95% CI: 38-78 mg/kg per day) and 80 mg/kg per day (95% CI: 40-119 mg/kg per day) for term and preterm infants, respectively.

CONCLUSION

The determined mean phenylalanine-requirement estimates are lower than the contents of term and preterm formulas currently on the market. This trial was registered at www.trialregister.nl as NTR1610.

Tryptophan requirement of the enterally fed term infant in the first month of life

OBJECTIVES

Tryptophan not only is an amino acid essential to protein synthesis but also serves as a precursor in 2 important metabolic pathways: the serotonin and the kynurenine pathways. Tryptophan is related to sleeping patterns. The objective of the present study was to determine the tryptophan requirement of term infants using the indicator amino acid oxidation (IAAO) method with L-[1-C]phenylalanine as the indicator.

METHODS

Enterally fed infants were randomly assigned to tryptophan intakes ranging from 0.5 to 73 mg · kg · day as part of an elemental diet. After 1-day adaptation to the test diet, [C]bicarbonate and L-[1-C]phenylalanine tracers were given enterally. Breath samples were collected at baseline and during isotopic plateaus. The mean tryptophan requirement was determined by using the biphasic linear regression crossover analysis on the fraction of CO2 recovery from L-[1-C]phenylalanine oxidation (FCO2). Data are presented as mean ± standard deviation.

RESULTS

A total of 30 term neonates (gestational age 39 ± 1 weeks) were studied at 9 ± 4 days. FCO2 decreased until a tryptophan intake of 15 mg · kg · day; additional increases in tryptophan intake did not affect FCO2. Mean requirement was determined to be 15 mg · kg · day.

CONCLUSIONS

The mean tryptophan requirement for elemental formula-fed term infants is 15 mg · kg · day. This requirement is lower than the present recommended intake of 29 mg · kg · day, which is based on the average intake of a breastfed infant.

Branched-chain amino acid requirements for enterally fed term neonates in the first month of life

BACKGROUND

Knowledge of essential amino acid requirements in infants is important because excessive intake of protein can lead to increased long-term morbidity such as obesity. A deficient intake may lead to suboptimal growth and impaired neurodevelopment. The current recommended branched-chain amino acid requirements in infants aged 0-1 mo are based on the amino acid content of human milk.

OBJECTIVE

We quantified the requirements for isoleucine, leucine, and valine for term neonates by using the indicator amino acid oxidation method with [1-(13)C]phenylalanine as the indicator.

DESIGN

Fully enterally fed term infants received randomly graded amounts of isoleucine (5-216 mg · kg(-1) · d(-1)), leucine (5-370 mg · kg(-1) · d(-1)), or valine (5-236 mg · kg(-1) · d(-1)) as part of an elemental formula. Data are expressed as means ± SDs.

RESULTS

Eighty-three Asian, term neonates (mean ± SD birth weight: 3.3 ± 0.4 kg; gestational age: 39.4 ± 1.3 wk) were studied at a postnatal age of 13 ± 5 d. Mean requirements for isoleucine, leucine, and valine (measured in boys only) were 105 mg · kg(-1) · d(-1) (r(2) = 0.61, P < 0.001), 140 mg · kg(-1) · d(-1) (r(2) = 0.26, P < 0.01), and 110 mg · kg(-1) · d(-1) (r(2) = 0.35, P = 0.001), respectively.

CONCLUSIONS

Current human milk-based recommendations for isoleucine and valine in term infants aged 0-1 mo are correct. However, the current recommendation for leucine (166 mg · kg(-1) · d(-1)) is higher than the mean requirement of 140 mg · kg(-1) · d(-1) that we determined in this study. This trial was registered at www.trialregister.nl as NTR1610.

Compositional requirements of follow-up formula for use in infancy: recommendations of an international expert group coordinated by the Early Nutrition Academy

The follow-up formula (FUF) standard of Codex Alimentarius adopted in 1987 does not correspond to the recently updated Codex infant formula (IF) standard and current scientific knowledge. New Zealand proposed a revision of the FUF Codex standard and asked the non-profit Early Nutrition Academy, in collaboration with the Federation of International Societies for Paediatric Gastroenterology, Hepatology, and Nutrition (FISPGHAN), for a consultation with paediatric nutrition experts to provide scientific guidance. This global expert group strongly supports breastfeeding. FUF are considered dispensable because IF can substitute for breastfeeding throughout infancy, but FUF are widely used and thus the outdated current FUF standard should be revised. Like IF, FUF serve as breast milk substitutes; hence their marketing should respect appropriate standards. The compositional requirements for FUF for infants from 6 months onwards presented here were unanimously agreed upon. For some nutrients, the compositional requirements for FUF differ from those of IF due to differing needs with infant maturation as well as a rising contribution of an increasingly diversified diet with advancing age. FUF should be fed with adequate complementary feeding that is also appropriate for partially breastfed infants. FUF could be fed also after the age of 1 year without safety concerns, but different compositional requirements should be applied for optimal, age-adapted milk-based formulations for young children used only after the age of 1 year. This has not been considered as part of this review and should be the subject of further consideration.